Optimization of ultrasound-assisted extraction of total polyphenolic compounds from Juglans nigra L. leaves

Abstract

The ultrasound-assisted extraction of Juglans nigra L. leaves was optimized with respect to total phenolic content (TP) of the extracts by varying the concentration of aqueous ethanol solution (E) and different solvent-to-solid ratio (S). The influence and optimum of the operating parameters (E and S) was examined using response surface methodology (RSM). The statistical criteria indicated the adequacy, reliability and precision of the developed RSM model. RSM showed that maximum extraction yield of TP 28.59 mg g-1 of draw plant was achieved at the optimal values of 50% E and 20 kg kg-1 S. Using the modelled optimized conditions, the detected relative difference between the predicted and the experimental yield was ±2.3 %. The determined TP content in the extracts varied from 12.54 to 29.26 mg GAE g-1 of dry plant indicated that J. nigra is a valuable source of phenolic substances. The extracts of J. nigra leaves obtained under optimal conditions showed good antioxidant activity (IC50 = 18.91±0.03 μg cm-3) which was determined by the scavenging effect on 2,2-diphenyl-1-picrylhydrazyl radical. The optimization of the TP extraction process is the important step in improving techno-economics of the potential commercial preparation of J. nigra extracts, as natural source of antioxidants.

Keywords

• black walnut
• polyphenols
• response surface methodology